So I screwed up the bootloader on my PC. Again. I was able to fix it but it's always a pain to borrow another computer to download an ISO of my favorite distro and prepare a USB stick to repair that every time.There's a neat application called DriveDroid that lets you use your phone as a USB drive for this exact purpose, but on my phone it was setting the gadget driver to the wrong mode, causing it to emulate a CDROM drive instead of a more conventional thumb drive (which Arch doesn't like), plus it's not open source, so I made my own application which is much faster and does things properly.

Source code and downloads are on GitHub (APKs in the releases tab, root is mandatory).

I tested it on my (2012 model) Nexus 7 and my OnePlus 2, not with my Nexus 4 though since it's on the unrooted stock ROM and I need to charge it as well. I've heard of a Nexus 5 and a OnePlus X working fine with it, so I presume compatibility should be fairly good.

This is very useful, i wasn't aware this was possible on Android !I do wonder if this can be used to mount other operating systems as well like FreeDOS for example...If so then there's no need to use Easy2Boot or buy a Gotek

I kind of wish i had this earlier because i too screwed up my mbr with an update.

CDROM mode would be useful for legacy type isos which expect booting from an actual CD unless you use something like unetbootin, but it's only available in newer kernels and I don't really want to overcomplicate this. It should work fine with anything you can dd straight to a USB stick though. Not sure about freedos.